Embodiments of the present disclosure relate generally to subcutaneous implantable medical devices and methods, and more particularly to medical devices having pulse generators and leads that are implanted subcutaneously.
Currently, implantable medical devices (IMD) are provided for a variety of cardiac applications. IMDs may include a “housing” or “canister” (or “can”) and one or more electrically-conductive leads that connect to the canister through an electro-mechanical connection. IMDs may contain electronics (e.g., a power source, microprocessor, capacitors, etc.) that control electrical activation of the leads to provide various functionalities. For instance, the IMD may be configured for pacemaking, cardioversion, and/or defibrillation. An implantable cardioverter-defibrillator (ICD) is one such medical device and it is designed to monitor heart rate, recognize certain events (e.g., ventricular fibrillation or ventricular tachycardia), and deliver electrical shock to reduce the risk of sudden cardiac death (SCD) from these events. The ICD may be used for patients who have already experienced potentially life-threatening events or for those that are at risk of SCD. The ICD includes a pulse generator and one or more leads having electrodes that may be used to detect how the heart is functioning or provide electrical shock to the heart.
One type of ICD delivers therapy through transvenous leads that are advanced to the right ventricle for detection and treatment of tachyarrhythmia. Transvenous ICDs (or TV-ICDs) may also provide bradycardia-pacing support. Although TV-ICDs can be helpful and prevent sudden cardiac death, TV-ICDs may have certain drawbacks or potential complications. For instance, it can be difficult and time-consuming to achieve venous access, thereby prolonging the medical procedure. TV-ICDs can be associated with hemopericardium, hemothorax, pneumothorax, lead dislodgement, lead malfunction, device-related infection, and venous occlusion. Transvenous leads may also malfunction through conductor failure in the leads or breaches in the insulation that surrounds the conductors.
A second type of ICD, referred to as a subcutaneous ICD (or S-ICD), uses an electrode configuration that can reside entirely within the subcutaneous space. The pulse generator is positioned along a side of the patient's chest below the arm pit (e.g., over the sixth rib near the left mid-axillary line). A lead extends from the pulse generator along the side of the patient toward the sternum. The lead then turns to extend parallel to the mid-sternal line and is positioned adjacent to the sternum extending between the xiphoid process and the manubriosternal junction. This portion of the lead includes a shock coil that is flanked by two sensing electrodes. The sensing electrodes sense the cardiac rhythm and the shock coil delivers counters-hocks through the subcutaneous tissue of the chest wall. Unlike the transvenous types, the S-ICDs lack intravenous and intracardiac leads and, as such, are less likely to have the noted complications associated with more invasive devices. Current electrode configurations for S-ICDs, however, have some challenges or undesirable features. For instance, conventional commercially available as ICDs are relatively large and exhibit higher defibrillation threshold (DFTs), as compared to modern transvenouSIMDs. For example, a conventional S-ICD may be 60-70 mL in volume, as compared to a 30 mL transvenouSIMD. As another example, a conventional S-ICD may utilize DFTs of 80 J, as compared to 40 J for transvenouSIMDs. A desire remains to further improve upon the size and energy demands of S-ICDs.